Are Your Photographs Sharp or Just Acceptably Sharp?

Posted on Mar 23, 2018

Today’s Post by Joe Farace

“If the point is sharp, and the arrow is swift, it can pierce through the dust no matter how thick.”—Bob Dylan

When I updated my old computer to a 5K iMac it changed the way I view and work with older images. Photographs that were made with older, lower resolution digital cameras and then viewed on older, softer CRT monitors don’t compare with how they looked today on higher resolution, crisp and contrasty LCD monitors.

It’s also changed my workflow: When looking at photographs on the 5K monitor I confronted two different situations: How bad some of them looked and not just because of resolution but what appeared acceptably sharp on a CRT monitor looks unacceptably soft at 5K. On the other hand, some of my sharper images literally leaped off the screen.

The basic laws of imaging state that only one part of a three-dimensional object can be in focus at the image plane. This means areas that the space in front of and behind the focus plane still appear more or less in focus or in acceptable focus. That’s what depth-of-field is all about.

Depth-of-field is an area that your eyes perceive as being in focus and is affected by several things. Depth-of-field increases as the lens’ aperture is stopped down, decreases as the aperture gets larger and the camera to subject distance decreases. At the point of critical focus, there is a range of acceptable focus that is one-third in front of that point and two-thirds behind it.

Which is why, especially when shooting infrared, like the above image, I use Hyperfocal focusing. The Hyperfocal Distance is the specific point of focus where any object between that distance and infinity is in focus. While its a gradually disappearing feature, some lenses still have an aperture ring. Most vintage lenses even have a depth-of-field scale, which can be helpful when using hyperfocal focusing. Here’s how it works with manual focusing lenses like Voigtlander’s Nokton 10.5mm f/0.95 lens that was used to make the above photograph: You select an aperture on the lens, then rotate the focusing ring setting so that aperture appears opposite the infinity mark on the lens’ depth-of-field scale.